Background of the Invention

This invention relates generally to a system and method for addressing a plurality of sensors in an array, and in particular, to a system and method for addressing a plurality of resistive sensors.

A number of different types of sensing devices have been used to sense various characteristics about a three-dimensional object. For example, one type of sensing device may be used to determine the surface contour of a three-dimensional object. Some

surface contour sensing devices use a single probe head that is moved across the surface of the object. These probe head systems are very slow and expensive.

Another way to measure the surface contour of a three-dimensional object is to use a device that may measure the contour of an entire side of the object. One such device is a sensing device that may have a plurality of sensors arranged in an array so that an entire side of the three-dimensional object may be measured. These devices employ an array of sensors and are especially useful for larger objects. In addition, these systems are

less expensive and quicker than probe head systems.

These sensing devices having an array of sensors may use an array of analog-type resistive sensors, such as potentiometers, strain gauges, thermocouples and similar

sensors that measure the resistance of the sensor to determine a characteristic of the object. Each sensor in the array must be individually addressed so that the resistance of each sensor may be measured.

Conventional sensing devices with an array of resistive sensors address each sensor in the array separately by using two addressing lines for each sensor. The individual addressing of each sensor permits this system to independently and selectively measure the resistance of each sensor. However, this addressing system has several drawbacks. First, the process of measuring the resistance of each sensor in the array is time consuming because each sensor must be individually addressed. Second, since each resistive sensor requires two addressing lines, a very large number of addressing lines are required. For example, for a 100 sensor array, 200 addressing lines are needed. Third, resistive sensors always have some resistance so that come current may leak through the resistors. This current leakage distorts the measurement of the resistance of each sensor so that a sensing device using this addressing system will have poor accuracy.

In summary, conventional addressing systems for an array of resistive sensors are slow due to the large number of sensors that need to be addressed, have a large number of actual addressing lines, and make the sensing devices that use these conventional

addressing systems less accurate due to leakage of current through the resistive sensors.

Thus, there is a need for a system and method for addressing a plurality of resistive sensors which avoid these and other problems of known devices, and it is to this

end that the present invention is directed.

Summary of the Invention

The invention provides an addressing system for an array of resistive sensors that

is faster since individual addressing lines for each resistive sensor are not needed. In addition, the invention provides an addressing system for an array of resistive sensors wherein there is less current leakage through the resistive sensors which makes the

measurement, conducted by the sensing device using the addressing system, more

accurate. The addressing system for an array of resistive sensors also may reduce the complexity of the addressing system since fewer addressing lines are required.

The addressing system in accordance with the invention may have a plurality of

sensors, each sensor having a variable resistance that assumes a predetermined value in accordance with a characteristic of an object being measured by the sensor, and the sensors are arranged in an array having rows and columns. The system addresses a

predetermined sensor in said array by applying a first predetermined voltage to select a

particular row of sensors having said predetermined sensor and by applying a second predetermined voltage to select a particular column of sensors having said predetermined sensor. The system also limits the current thorough sensors in the array that are not said

predetermined sensor. A method of addressing a sensor within an array of sensors is also provided.

Brief Description of the Drawings

Figure 1 is a block diagram showing a sensing system that may use an addressing system in accordance with the invention;

Figure 2 is a enlarged schematic view of a sensing array of Figure 1;

Figure 3 is a schematic diagram of an example of an array of resistive sensor elements; and

Figure 4 is a schematic diagram of the addressing system in accordance with the invention that may be used with the resistive sensor array of Figure 3.

Detailed Description of a Preferred Embodiment

The invention is particularly applicable to an addressing system for an array of resistive sensors, such as potentiometers. It is in this context that the invention will be described. It will be appreciated, however, that the system and method in accordance with the invention has greater utility.

A device for measuring a characteristic of a three-dimensional object, such as the surface contour, may use an array of resistive sensors to measure the characteristic. Each of these resistive sensors may have a resistance that changes depending on the changing

characteristic of the object. For example, a surface of the object that has more height may correspond to a lower resistance of the resistive sensor that is located over that surface.

The resistance values for each of the sensors needs to be measured so that the

characteristic of the object may be determined. To measure each of these resistive sensors, a system for addressing each of these resistive sensors is needed. The invention provides an addressing system that may be used to address an array of resistive sensors.

To better understand the addressing system, a sensing system in which the addressing

system may be used will be described.

Figure 1 is a block diagram of a sensing system 20 that may incorporate the

addressing system in accordance with the invention. The sensing system 20 may include a

sensing device 22 that may have a frame 23 and a plurality of sensors 24. The sensing device may be used to measure the characteristic of a three dimensional object 26, that may be, for example, a vase. The frame of the sensing device may secure the plurality of

sensors into an array of sensors. Each of the sensors may be a resistive sensor, such as a potentiometer, a strain gauge, a thermocouple, or other sensors whose resistance varies depending on the measured quantity. Each of the sensors in the array may be addressed by an addressing system 28. The addressing system, as described below in more detail,

may address the array of sensors quickly, with less actual addressing lines, and with less

current leakage than conventional addressing systems. The addressing system may also convert the measured resistance of each of the sensors into an analog electrical signal, and

the analog electrical signal of the addressing system may be converted to a digital signal by an analog to digital converter (A/D) 30.

The electrical digital output of the A/D converter may be fed into a computer interface 32 that interprets the digital signals and may generate, for example a representation of the object on a computer system 34 that may have a computer display 36. The array of resistive sensors will now be briefly described.

Figure 2 is a schematic diagram of the sensing device 20 that may be addressed by the addressing system in accordance with the invention. The sensing device has the frame 23 and the plurality of sensors 24. As shown, the frame may hold the sensors so that there may be a predetermined spacing between the sensors. These sensors form an array of sensors. The addressing system in accordance with the invention may address in not limited to any particular size or shape of array. Now, an array of resistive sensors will be described.

Figure 3 is a schematic diagram of an array 50 of resistive sensors that may be addressed by the addressing system in accordance writh the invention. The invention, however, is not limited to the particular type of resistive sensors shown and may be any other type of resistive sensor, such as a potentiometer, a strain gauge, or a thermocouple.

The array 50 may have at least one row 52 of sensors and at least one column 54 of sensors. The array may have at least one variable resistance sensor 56. Each resistive

sensor may have a first electrical contact 58 and a second electrical contact 60, and a

third electrical contact 62. In this example, the resistive sensors are shown as resistors

and the first and third electrical contacts are located at each opposing end of the resistor. In addition, since the resistance of these variable resistors changes, the second electrical contact 62 that may be connected to, for example, the resistance varying portion of the

resistor. Thus, contact may be made to each end of the resistor and the resistance varying portion of the resistor. Now, an addressing system in accordance with the invention for addressing an array of resistive sensors will be described.

Figure 4 is a schematic diagram of an addressing system 28 in accordance with the invention for an array 50 of resistive sensors. As described above, the array 50 may have

at least one row 52 of sensors, and at least one column 54 of sensors. In the example

shown, there are five rows and five columns of sensors for a total of 25 sensors. The invention, however, is not limited to any particular number of sensors, or any particular size of array. Each sensor 56, as described above, may have the first electrical contact 58, a second electrical contact 60 and a third electrical contact 62. In addition, a current

limiter 64 may be connected to the first electrical contact 58 of each sensor 56. The

current limiter may preferably be a diode, but may also be any other type of current limiting device. The preferred diode may be a switching diode, such as model number BAS19 made by Diodes, Inc. The current limiter permits current to flow through the

resistor from the first electrical contact 58, however it limits the amount of current that may leak from a sensor back through the current limiter even when the sensor has not

been addressed. The operation of the diode is well known in the art and will not be described here. Without the current limiter, the measured resistance values of any of the sensors in the array, as described in more detail below, are distorted. The current limiter may preferable be incorporated into the addressing system. The addressing system will now be described.

The addressing system may have a first addressing sub-system 70 that may be address each row 52 of the array. The first addressing sub-system may include a switching system 72, such as a multiplexer and a plurality of address lines 74 connected to the multiplexer. The preferred multiplexer may be an 8 X 1 Analog Multiplexer/Demultiplexer, such as model number CD4051BCN manufactured by National Instruments, Inc. The multiplexer, as is known in the art, may select one of the addressing lines 74 based on control signals received from a digital controller that is not shown. The digital controller may be, for example, a processor in a computer system, or a processor located within the sensing device. The multiplexer 72, for example, may select a first addressing line 75 that may select the first row of sensors. When a row of sensors are selected by the first addressing sub-system 70, a positive voltage may be provided, through the current limiter 64, to the first electrical contact 58 of each sensor in the row. In this example, the positive voltage is provided by a +5 volt power supply 76. The line that provides the positive voltage to the multiplexer also connects to an analog to digital converter 78 that may be used to measure the resistance of the sensor by measuring the current drawn by the resistor. The analog to digital converter may convert the analog

current signal to a digital signal which is then fed into a computer interface (not shown).

The computer interface then may convert the current signal into a resistance value in a

well known manner. The computer interface may have a high impedance buffer so that the voltage applied to the sensors is not altered by the computer interface. To select a particular sensor within the selected row, a second addressing sub-system 90 is provided.

The second addressing sub-system 90 may have a switching device 92, such as a multiplexer and a plurality of addressing lines 94. The preferred multiplexer may be another 8 X 1 Analog Multiplexer/Demultiplexer, such as of the same type as the

multiplexer in the first addressing sub-system. The multiplexer, as is known in the art,

may select one of the addressing lines 94 based on control signals received from a digital

controller that is not shown. The digital controller may be, for example, a processor in a

computer system, or a processor located within the sensing device. The second

addressing sub-system selects a particular column of sensors based on the digital control signals. For example, a first addressing line 95 selects a first column of sensors. When the column of sensors are selected by the multiplexer, a ground potential 96 may be

connected to the second electrical contact 60 of each sensor within a column.

To select a particular sensor 100, the first addressing sub-system 70 selects the first addressing line 75 connected to the first row of sensors and the second addressing

sub-system 90 selects the first addressing line 95 connected to the first column of sensors. The third electrical contact 62 of each resistor is not connected to anything. Thus, only

the particular sensor 100 will have a positive voltage applied to its first electrical contact and a ground potential applied to the second electrical contact. The resistance of that particular sensor may then be measured by measuring the current flowing through the resistor. The resistance of the sensor may then be measured by converting the measured current into a resistance, as is known in the art. To measure the resistance of a second sensor 102 in the first row, a different addressing line is selected by the column multiplexer 92 so that the second column of the sensors are selected. In this manner, the entire array of sensors may be addressed.

This resistive sensor addressing system uses fewer addressing lines than conventional resistive sensor addressing systems. For example, a conventional twenty- five sensor array that addresses each sensor individually would need 50 total lines to address the 25 sensors. By contrast, the addressing system in accordance with the invention will need only 10 addressing lines. As the number of sensors within the array increases, the disparity between the invention and conventional addressing systems becomes more pronounced. For example, for an array with 1024 sensors ( a 32 X 32 array), 2048 addressing lines would be required in a conventional resistive sensor addressing system, but only 64 addressing lines are needed for the addressing system in

accordance with the invention.

In addition, the addressing system limits the current that may leak from sensors that are not currently being addressed by the current limiter. The current leakage of the

sensors occurs because resistive type sensors are analog devices that may have any number of resistance values, and may not have a resistance of zero. Thus, any time that a resistive sensor is connected to a power supply, some current may flow through the resistive sensor due to the non-zero resistance. Thus, in an array of sensors where a row of sensors is addressed and connected to a positive voltage, each of the sensors in the row or column may cause some current leakage. The sensor that is being measured does not have a current leakage because the other end of that sensor is connected to a ground potential. To limit the current leakage of the sensors not being measured, the current limiter may be used. Without the current limiter, the leakage current causes the measurement of the current flowing through the desired resistive sensor to be distorted which distorts the resistance measurement as well. With the addressing system in accordance with the invention, a voltage drop across the non-selected resistors is prevented because current may not leak from the resistive sensor back through the addressing line so that the measured resistance is not distorted.

While the foregoing has been with reference to a particular embodiment of the invention, it will be appreciated by those skilled in the art that changes in this embodiment may be made without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims.